1. Field of the Invention
The present invention relates to a method and an apparatus for functional monitoring of a catalytic converter for cleaning exhaust gas. As emissions regulations become evermore stringent all over the world, it becomes necessary to monitor the function of catalytic converters in motor vehicles either constantly or at least periodically, so that if a catalytic converter can no longer perform its function that will be determined early.
International Patent Application WO 91/14855, corresponding to U.S. Pat. Nos. 5,255,511 and 5,307,626; and International Application WO 92/03643, corresponding to U.S. Pat. No. 5,355,671, disclose various configurations with temperature sensors that are used to monitor catalytic converters. Evaluation methods for the measured values attained with the measurement sensors are also described. The earlier measurement concepts have to do essentially with functional monitoring of a catalytic converter that is at an operating temperature, or in other words that is at a temperature markedly above the temperature at which the catalytic conversion begins. However, in view of stringent exhaust gas regulations for the total emissions of a motor vehicle, it has been found that catalytic converter performance in the cold starting phase, in particular, or in other words within the first minute after the starting of an internal combustion engine, plays an especially decisive role. In order to evaluate the functional capability of a catalytic converter, it is also important to know when the catalytic conversion in the catalytic converter begins, and possibly also at what temperature.